Biological Evidence

Domestic dogs interbreed with three wild canid species: coyotes, jackals, and wolves. Charles Darwin (1875/1988) discusses at length in The Variation of Animals and Plants Under Domestication that the variability and diversity of the dog could only be adequately explained by postulating an admixture of several wild species represented in the canine genome. Following in the tradition of Darwin, Konrad Lorenz (1954) also argued that domestic dogs owe their genetic endowment to a combination of canid bloodlines. He believed that the dog was first domesticated from the jackal (Canis aureus) and only later crossed with the wolf. However, upon subsequent reexamination of the behavioral evidence, Lorenz (1975) reassessed and reformed his theory by substituting Canis lupus pallipes in place of the jackal. An important factor affecting his change of opinion was the finding that jackals are much less sociable and exhibit a distinctive howling pattern not shared by dogs.

"The wolf, disarmed of ferocity, is now pillowed in the lady's lap." This speculation written by Edward Jenner in 1798 has turned out to be true. The genetic and behavioral evidence to date points uniformly to the wolf as the exclusive wild progenitor of the dog. Supporting this view is the fact that both dogs and wolves share a very similar genotype and readily interbreed. Testifying to the ease with which wolves and dogs interbreed is the growing population of wolf-dog hybrids. It has been roughly estimated that approximately 300,000 wolf-dog hybrids are currently kept as companion animals in the United States (Clifford and Green, 1991), although these numbers have been disputed and remain controversial.

Robert Wayne (1993) has confirmed the close genetic relationship between dogs and wolves by comparing the mitochondrial DNA sequences of wild canids and dogs. According to this line of research, dogs are domesticated wolves with only slight genetic alterations affecting developmental timing and growth rates: "Dogs are gray wolves, despite their diversity in size and proportion; the wide variation in their adult morphology probably results from simple changes in developmental rate and timing" (1993:220). Both wolves and dogs possess 78 chromosomes (Table 1.1). Comparisons of canid DNA sequences reveal that dogs are more closely related to wolves than to coyotes. Al

Table 1.1. The diploid chromosome numbers for canids showing a close relationship between the dog, wolf, coyote, jackal, and other canids

Species

Common name

Range

Chromosomes

Canis aureus

Golden jackal

Old World

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